The size of the list, typically used to check people entering the country through land border crossings, airports and sea ports, has been growing by 200,000 names a year since 2004. Some lawmakers, security experts and civil rights advocates warn that it will become useless if it includes too many people.

'It undermines the authority of the list,' says Lisa Graves of the Center for National Security Studies. 'There's just no rational, reasonable estimate that there's anywhere close to that many suspected terrorists.'"